The current market offers many different kinds of filter bags (or tea bags) for infusing the above mentioned products in water.
The wide range of filter bags currently available is the result of the increasingly widespread use and popularity of filter bags among consumers, both in the home and in public places, which has led to a growing demand, especially from product distributors, for diversification of filter bag designs with a view to obtaining filter bags with improved properties in terms of product containment, ease of exchange with the liquid during infusion, shelf life, ease of final packaging, and so on.
The two main designs currently used are the traditional single-lobe bags (usually with tie string and tag) and the now well-established two-lobe bags (also with tie string and tag, with or without individual overwrapper), whose characteristic feature is the larger surface area in contact with the liquid, which allows optimum extraction of the flavour from the infusion product).
Over the years, both these designs have been made from different types of filter paper, including, more recently, biodegradable products.
Similarly, the methods of closing the bag and simultaneously applying the string and tag (in designs where these are present) have been diversified according to production needs and, in some countries, legislative requirements: for example, the tie string, tag and filter bag may be closed and joined by a metal staple, by gluing, by a heat sealable “accessory stamp”, by forming a stitch with the tie string itself or by using an adhesive tag.
All of these have improved the quality of filter bags, the processes used to manufacture them (filter bag making machines) and end user satisfaction.
Continuing its policy of product improvement, however, the Applicant has noticed that current filter bags, especially single-lobe bags (which this invention is concerned with in particular) have inherent shortcomings due to their shape which, precisely because they have a single chamber, tend to lack adequate three-dimensional, or volumetric, properties. The resulting disadvantages are that:                the product is more constrained within the bag, with less room to expand during infusion, which means poorer quality infusions and longer infusion times;        flattening causes the surfaces of the filter bags to become misshapen;        the filter bags are more difficult to pack on account of possible movements during positioning.        
Flattening and movement of the filter bags may damage and reduce the overall quality of the product contained.